Fire alarm switch



May 3, 1949. J. w. ALBRECHT 2,469,024 l FIRE ALARM SWITCH Filed March 6, 1947 QW@ H l5 ATTO EYS.

Patented May 3, 1949 FIRE ALARM SWITCH Jacob W. Albrecht, Queens Village, N. Y., assigner to Dictograph Products Company, Inc., New York, N. Y., a corporation of Delaware Application March 6, 1947, Serial No. 732,704

(Cl. ZOU-142) 2 Claims.

This invention relates to fire alarm switches,`

and has particular reference to systems which are thermally responsive to a high degree of local heat for sounding an alarm, preferably electrically.

By their nature, fire alarm systems are seldom activated and their long inactive periods frequently result in deterioration of essential parts so that they are no longer as reliable as required. Many systems have no means for periodic testing, so that it is impossible to know Whether or not they are in good operating condition or will be reliable when a fire occurs.

In accordance with the present invention, a thermo-electrical re alarm is provided which is reliable, may be simply tested periodically, and is so constructed that positive electrical connection is made at the scene of the fire for energizing a remote signal located at the alarm station.

In a preferred embodiment of the invention, an electric bell and a local battery are connectible through any one of a plurality of normally open, mutually remote sets of contacts arranged in parallel, each set being held open by a fusible element which releases them to close the alarm circuit. Each contact set is also short-circuitable at will by a manual button for sounding the bell for test purposes. Specically, the several contact sets are leaf springs, each mounted at one end with the free ends held apart by the fusible element, which is responsive to a predetermined degree of heat to release the contacts as described. The contact portions of the corresponding springs are bent toward each other to form knife-like edges and are arranged at an angle to each other, so that upon release of the retracted spring by the fusible part, the knife-like edges engage with a wiping action so that circuit closure is assured and sounding of the alarm results.

It will be seen that the fire alarm system of this invention is extremely simple in construction and operation, is not likely to get out of order, is virtually immune from disabling deterioration and may be readily tested Without disturbing the alarm system.

For a more complete understanding of the invention, reference may be had to the accompanying drawings, in which:

Figure 1 is a simplified wiring diagram of the iire alarm system orf this invention;

Fig. 2 is a face view of the interior of one of the thermo-responsive units;

Fig. 3 is a longitudinal section therethrough, as seen along the line 3-3 of Fig. 2; and,

Fig. 4 is an enlarged cross-section through the contact spring, showing the manner in which they are held normally separated by the fusible element.

Referring to Fig. 1 of the drawings, numeral II) designates an electric bell of conventional construction, one terminal of whose magnet Winding II is connected to a source of ringing current, preferably a local -battery I2, and whose other terminal is connected to Wire I3 leading to the parallel remote thermo--responsive units I4. Two of such units are shown, although many more may be used, each located on the point of possible re, such as in a furnace room, kitchen, laundry, and the like.

Each thermo-responsive unit I4 comprises a suitable casing I5 containing a pair of contact springs I6 and Il, connected respectively to Wire I3 and a return Wire I8 to battery I2. Springs I6 and I1 are of the leaf spring type, anchored at one end in the casing I5 with their free ends bent toward each other and arranged at an angle to form the knife-edge contacts I6 and Il', as shown especially in Figs. 2, 3 and 4. These contacts I6 and I'l are normally urged into engagement by the resiliency of their springs I6 and II, -which are bent as shown in Fig. 3.

The contacts I6' and I'I are normally held disengaged by the fusible element I9, which retracts spring I6 in the manner shown in Figs. 3 and 4. Fusible element I9 consists of a strut 20 and a bridge 23 soldered together at F with a fusible metal, such as a Woods alloy, arranged to fuse at a predetermined high temperature such as about F., more or less, depending on requirements. Strut 20 is a at strip formed into, or otherwise provided with a lateral hook 2l at one end, which is passed through a narrow slot 22 in spring I6, turned a quarter turn so as to catch the spring I6 with its hook 2|. The spring is then retracted toward the inner surface of the casing I5 and held in this retracted position by the bridge 23 which is adapted to span the opening 24 in casing I5 through which the strut 20 passes, as shown particularly in Figs. 3 and 4. In this way, although contacts I6 and Il are biased toward closed position by their respective springs I6 and I1, they are normally held open by fusible element I9. The element I9 is thus readily emplaced to separate the contacts I6 and Il and may be as readily replaced.

Secondary contacts 25 and 26 are also formed on contact springs I6 and I1, respectively, and

are normally open regardless of the condition of contacts I6 and I1'. A button 21 passing through the front of casing I is adapted to close these contacts 25 and 26 upon pressure, so as to temporarily short-circuit contact springs IG and II, thus closing s, signal circuit to the bell I0.

In operation of the system illustrated in Fig. 1, a predetermined high degree of heat in the vicinity of one of the thermo-responsive units I4 causes the fusible metal F, normally holding the strut 20 and bridge 23 of the element I9 together, to soften sufliciently that it can no longer hold strut 20 and bridge 23 together, whereupon spring I5 is released and its contact I6 engages opposed contact I'I with a wiping movement ,afforded by the resiliency of both springs. Because of this wiping movement and the narrowness of the edges I6 and I'I, they rub together and clean their surfaces so as to insure electrical circuit-closing contact. This causes bell I0 .to sound and give the alarm, and the bell continues to sound until shut 01T by disconnecting one of the wires I3, I4 or the bell I0 from its battery I2. This necessity of performing one of these disconnection acts is desired in order to insure no possibility of interference with the system, as might occur if a shutoi switch were provided. For the same reason, a battery is preferred as the source of ringing current, in order that the system is self-contained and its functioning cannot be impaired by failure of electric service, which is often shut off or disconnected during a re.

It will be observed that the battery I2 is normally not connected, so that no current is drawn and it lasts for a long time. Battery cells having a long shelf life are selected to the same end, and by employing mercury oxide cells, say three, a very compact alarm unit that can be housed. in a small, light Wall box is provided.

The test button 27 enables checking because the contacts 25 and 26 short-circuit the thermallycontrolled contacts I6 and I'I. Thus, if the bell E0 rings when a button 2l is pressed, it indicates that the circuit and power source for that particular thermal unit I4 are in operating condition. Because the short-circuiting test circuit is independent of the thermal combination I6', I1', I9, the thermal system is not disturbed when testing with buttons 21.

Although g preferred embodiment of the invention has been illustrated and described herein,

4 it is to be understood that the invention is not limited thereby, but is susceptible of changes in form and detail within the scope of the appended claims.

I claim:

l. A switch comprising a. support, a first leaf spring having a fixed end and a free end, said fixed end being mounted on the support and said free end carrying a first knife-like contact, a second leaf spring having a fixed end and a free end, said xed end being mounted on the support and said free end carrying a second knife-like contact at an angle to said rst contact, said `second spring being biased for engagement of said second contact with said first Contact, and a thermo-responsive element holding said second leaf spring retracted from said first leaf spring for release upon exposure of said element to a predetermined high temperature.

2. A switch comprising a support, a first leaf spring having a fixed end and a free end, said iixed end being mounted on the support and said free end carrying a first knife-like contact, a second leaf spring having a xed end and a free end, said fixed end being mounted on the support and said free end carrying a second knife-like contact at an angle to said first contact, said second spring being biased for engagement of said second contact with said rst contact, and a thermo-responsive element intermediate the fixed and free ends of the second leaf spring for holding said second leaf spring retracted from said rst leaf spring for release upon exposure of said element to a predetermined high temperature.

JACOB W. ALBRECHT.

REFERENCES CITED The following references are of record in the file or this patent:

UNITED STATES PATENTS Number Name Date 1,095,382 Clorius May 5, 1914 1,181,705 Weber May 2, 1916 1,500,399 Lanese July 8, 1924 1,597,822 Ramsey Aug. 31, 1926 1,745,735 Burdick Feb. 4, 1930 1,735,846 Brand Apr. 8, 1930 1,772,127 Brouty Aug. 5, 1930 1,986,507 Knight Jan. 1, 1935 2,105,113 Gibson Jan. 11, 1938 

